This invention relates to a process for starting up a fixed bed ethylene oxide reactor containing a supported silver catalyst promoted with one or more alkali metal promoter(s) which involves heating the reactor to slightly below normal operating conditions, passing an ethylene containing gas over the catalyst, adding a chlorohydrocarbon moderator to the gas passing over the catalyst and after approximately 0.1-5 milliliters of moderator (basis liquid) per cubic foot of catalyst has been added, then adding oxygen to the gas passing over the catalyst to initiate the ethylene oxidation reaction and subsequently raising the reactor temperature and gas flow rates to operating conditions.

Patent
   5155242
Priority
Dec 05 1991
Filed
Dec 05 1991
Issued
Oct 13 1992
Expiry
Dec 05 2011
Assg.orig
Entity
Large
39
12
all paid
1. A process for starting up a fixed bed ethylene oxide reactor containing a catalyst consisting essentially of silver and one or more alkali metal promoter(s) supported on an alumina carrier, which process comprises:
a) heating the reactor to a temperature between about 350° F. and 475° F.,
b) passing an ethylene-containing gas over the catalyst in the reactor,
c) adding a chlorohydrocarbon moderator to the gas passing over the catalyst and after an amount of moderator containing the chlorine equivalent found in about 0.1 to about 5 milliliters (basis liquid) of ethyl chloride per cubic foot of the catalyst has been added, then
d) adding oxygen to the gas passing over catalyst, and adjusting the reactor temperature and gas flow rates to operating design conditions.
2. The process of claim 1 wherein in step b) the ethylene-containing gas is passed over the reactor at a flow rate above 5 percent of the design flow rate.
3. The process of claim 2 wherein in step b) the ethylene-containing gas is passed over the reactor at a flow rate above 15 percent of the design flow rate.
4. The process of claim 1 wherein in step b) the ethylene-containing gas also contains nitrogen or methane.
5. The process of claim wherein the chlorohydrocarbon moderator is a C1 to C8 chlorohydrocarbon.
6. The process of claim 5 wherein the chlorohydrocarbon moderator is a C1 to C4 chlorohydrocarbon.
7. The process of claim 6 wherein the chlorohydrocarbon moderator is a C1 or C2 chlorohydrocarbon.
8. The process of claim 7 wherein the chlorohydrocarbon moderator is selected from the group consisting of methyl chloride, ethyl chloride, ethylene dichloride, vinyl chloride and mixtures thereof.
9. The process of claim 8 wherein the chlorohydrocarbon moderator is ethyl chloride.
10. The process of claim 1 wherein in step c) from about, 0.5 to about 2 milliliters of moderator per cubic feet of catalyst been added.
11. The process of claim 10 wherein from about 1 to about 1.5 milliliters of moderator per cubic feet of catalyst has been added.
12. The process of claim 1 wherein in step c) the moderator is added over a period of time ranging from about 0.5 to about 15 hours.
13. The process of claim 1 wherein in step c) the moderator is added at a rate sufficient to maintain a concentration of about 1-10 ppmv in the gas passing over the catalyst.
14. The process of claim 1 wherein in step d) the reactor temperature and gas flow rates are raised to operating conditions over a period of time after the start of the oxygen addition ranging from about 24 hours to about 60 hours.
15. The process of claim 1 wherein nitrogen gas is passed over the catalyst prior to passing ethylene-containing gas of step b) over the catalyst.
16. The process of claim 15 wherein the nitrogen is passed over the catalyst for a period of time ranging from about 1/2 to about 7 days.

This invention relates to a process for starting-up a fixed bed ethylene oxide reactor containing a catalyst consisting essentially of silver and one or more alkali metal promoter(s) supported on an alpha alumina carrier.

A number of commercial ethylene oxide processes utilize a tubular reactor for converting ethylene to ethylene oxide. This fixed bed reactor typically utilizes a silver-based catalyst which has been supported on a porous support and which is typically promoted with one or more alkali metal promoter(s). The shell side of the ethylene oxide reactor typically utilizes a high temperature coolant to remove the heat generated by the oxidation reaction. Under operating conditions a chlorohydrocarbon moderator is utilized to control the oxidation reaction. Reactor product gases are passed through an ethylene oxide absorber and the overhead gases from the absorber, containing unreacted ethylene and ballast gas such as methane and other inerts are recycled back to the reactor with some carbon dioxide and inerts in the overhead stream being removed on the way back to the reactor.

The usual practice for starting up fresh silver/alkali metal-supported ethylene oxide catalysts in a commercial plant is to first add ethylene and diluent gas; then slowly introduce oxygen to get the reaction started; and then to gradually introduce chlorohydrocarbon moderator to control the reaction after it is producing enough heat to become self-sustaining. For the traditional silver-based, alkali-metal promoted supported catalyst, the chlorohydrocarbon moderator serves to decrease the activity (i.e., raise the temperature as required to obtain a given conversion level) while increasing selectivity to ethylene oxide. When utilizing conventional alkali metal-promoted, supported silver catalysts, the catalysts are very active at normal start-up temperatures. Chlorohydrocarbon moderator levels are introduced after start-up to control the high catalyst activity to reduce the conversion level, and to prevent a "run away".

The appearance of a new generation of ethylene oxide catalysts comprising silver/rhenium/alkali metal supported on alumina has presented start-up considerations considerably different than those presented by the conventional silver/alkali metal catalysts. As is illustrated in FIG. 1, the rhenium-containing catalysts have a completely opposite activity response to the presence of chloride-containing moderator than do the conventional catalysts. The rhenium-containing catalysts have an initial low activity, requiring a very high reactor temperature (as measured by the reactor coolant temperature) to operate properly. Since most commercial reactors cannot reach this required high temperature during start-up, special techniques have been evolved. U.S. Pat. No. 4,874,879, issued Oct. 17, 1989, discloses a method of prechloriding these rhenium-containing catalysts to enhance their activity and allow start-up at low temperatures. The prechloriding enhances the initial activity of the rhenium-containing catalyst. There is no indication in this patent that such prechloriding allows for a faster start-up or enhances the life of such rhenium-containing catalyst.

It has been found that the application of a prechloriding technique to the conventional silver/alkali metal-promoted alumina-supported catalyst, while decreasing the activity of the catalyst, allows for a faster start-up of the reactor, thus providing a significant cost advantage as well as extending the life of the catalyst.

This invention relates to a process for starting up a fixed bed ethylene oxide reactor containing a catalyst consisting essentially of silver and one or more alkali metal promoter(s) supported on an alumina carrier which process comprises a) heating the reactor to slightly below its normal operating temperature, b) passing an ethylene-containing gas over the catalyst, c) adding a chlorohydrocarbon moderator to the gas passing over the catalyst and after an amount of moderator containing the chlorine equivalent found in about 0.1 to about 5 milliliters (basis liquid) of ethylene chloride per cubic foot of the catalyst has been added, d) adding oxygen to the gas passing over the catalyst to start the oxidation reaction and raising the reactor temperature and gas flow rates to operating conditions. This process is applied to new or fresh catalysts, as well as to used catalysts that have been subjected to a prolonged shut-down period.

FIG. 1 illustrates the activity response as a function of chlorohydrocarbon moderator present in a reactor of the silver/alkali metal supported catalysts used in this invention and of the silver/rhenium/alkali metal supported catalysts of the prior art.

FIG. 2 illustrates the selectivity response of silver/alkali metal-promoted alumina-supported catalysts as a function of time after start-up which either have or have not been subjected to the prechloriding treatment of this invention.

PAC Catalyst

The catalyst that is used in the fixed bed reactor that is started up by the process of the instant invention consists essentially of silver and one or more alkali metal promoter(s) supported on an alumina carrier, preferably an alpha alumina carrier. Typical of these catalysts are those described in U.S. Pat. No. 3,962,136, issued June 8, 1976 and U.S. Pat. No. 4,010115, issued Mar. 1, 1977.

The catalysts used in the instant process comprise a catalytically effective amount of silver and a promoting amount of one or more alkali metal(s). Preferably the major amount of alkali metal promoter present is a higher alkali metal selected from potassium, rubidium, cesium and mixtures thereof. Most preferably the major amount of alkali metal is cesium. Combinations of alkali metals, such as cesium and lithium are quite suitable. Minor amounts of sodium and/or lithium may also be present. Concentrations of alkali metal (measured as the metal) between about 10 and 3000 ppm, preferably between about 15 and about 2000 ppm and more preferably between about 20 and about 1500 ppm by weight of total catalyst are desirable.

The process of the instant invention is applied to new catalysts as well as to aged catalysts that, due to a plant shut-down, have been subjected to a prolonged shut-in period.

When new catalysts are utilized it has been found useful to subject these catalysts to a high temperature treatment with nitrogen gas passing over the catalyst. The high temperature treatment converts a significant portion of the organic nitrogen-containing compounds used in the manufacture of the catalyst to nitrogen-containing gases which are swept up in the nitrogen stream and removed from the catalyst.

Typically, the catalyst is loaded into the tube reactor and by utilizing a coolant heater, the temperature of the reactor (as measured by the coolant temperature) is brought up to within 10° F. to 100° F. (6°C to 56°C), preferably to 20° F. to 50° F. (11°C to 28°C) below the normal operating temperature. Temperatures closer to the normal operating temperatures can be utilized, but in most cases the lower temperatures are adequate for the chloride pretreatment and subsequent start-up. In general, the reactor is heated to a temperature between about 350° F. (177°C) and 475° F. (246°C). For aged catalysts the reactor is heated to the upper temperature range, say between about 420° F. (216°C) and 475° F. (246°C).

A nitrogen flow, if utilized, is then passed over the catalyst at a flow rate typically above about 5 percent of the design flow rate, preferably above about 15 percent of the design flow rate, up to the full design flow rate. The nitrogen flow may be initiated before or during reactor heatup. The nitrogen gas is typically passed over the catalyst for a period of time ranging from about 1/2 of a day to about 7 days, preferably from about 1 to about 3 days. During this purge time the nitrogen stream is monitored for nitrogen-containing decomposition products from the catalyst. The start-up of used catalysts may or may not require the use of nitrogen, but it is frequently used. When nitrogen is not utilized, the reactor may be pressurized with ethylene, methane or other non-oxidizing gas.

After the nitrogen-containing decomposition products have been removed to a suitable low level, generally less than about 10 ppm, the recycle loop to the ethylene oxide reactor is then pressurized with ethylene and a suitable ballast gas such as methane or nitrogen in preparation for start-up. Concentrations of ethylene in the recycle loop are normally maintained at levels of about 5-20% mol. A gas flow rate above about 5 percent of design rate, preferably above about 15 percent of design rate, up to the full design rate, is maintained over the reactor. For those few commercial reactors that operate with once through flow without recycle, the flow rates typically will be at full design flow rates, with ethylene levels at about 5-20% mol.

A chlorohydrocarbon moderator is then added to the recycle gas stream being fed to the ethylene oxide reactor. The amount of chlorohydrocarbon moderator is added slowly over a period of several hours until an amount of chlorohydrocarbon moderator equivalent, based on the chloride content, to approximately 0.1 to about 5 milliliters, preferably 0.5 to about 2 milliliters and most preferably 1 to about 1.5 milliliters of liquid ethyl chloride per cubic foot of catalyst in the reactor bed has been added to the gas stream being fed to the reactor.

Suitable chlorohydrocarbons used as moderators comprise the C1 to C8 chlorohydrocarbons, that is compounds comprising hydrogen, carbon and chlorine. Preferably these chlorohydrocarbons are C1 to C4 chlorohydrocarbons and most preferably they are C1 and C2 chlorohydrocarbons. The chlorohydrocarbons may be optionally substituted with fluorine. Illustrative examples of these moderators include methyl chloride, ethyl chloride, ethylene dichloride, vinyl chloride and mixtures thereof. Preferred moderators are ethyl chloride, ethylene dichloride and vinyl chloride, particularly ethyl chloride.

Ethyl chloride, which is the preferred chlorohydrocarbon moderator, is used as the basis for calculating the amount of moderator that is to be passed over the catalyst. When a different moderator is to be used, the amounts can be calculated from the ethyl chloride amounts provided herein by adjusting for the differences in liquid densities and gram equivalent weights, basis chlorine, between ethyl chloride and such different moderator.

The moderator is added to the reactor during the prechloriding step preferably during a period of time ranging from about 0.5 to about 15 hours. These times, however, are not critical and shorter or longer periods can be used.

During the prechlorination process, chloride contents (basis ethyl chloride) in the recycle are typically maintained in the range of about 1-10 ppmv and the reactor is maintained at a temperature between about 350° F. (177°C) and 475° F. (246°C). Typically the reactor temperature during the prechlorination process will be maintained at about 10° F. to 100° F. (6°C to 56°C), preferably to 20° F. to 50° F. (11° C. to 28°C) below the normal operating temperature.

After the chlorohydrocarbon moderator has been fed to the catalyst in the above-specified amounts, oxygen is then added to the recycle feed stream at initially above about 5% of design rate, preferably above about 15% of design rate, up to the full design rate. Reaction initiation will occur within a few minutes of the addition of the oxygen, after which point the oxygen feed to the reactor, the feed gas to the reactor and the reactor temperature are raised to approximately the design conditions over a period of time ranging from about 24 hours to about 60 hours.

For purposes of illustration, the following Table 1 shows the range of operating conditions for which commercial ethylene oxide reactors units are designed.

TABLE 1
______________________________________
Broad Preferred
______________________________________
*GHSV, hour-1 1550-10000 2500-8000
Inlet pressure, psig
150-400 200-350
Inlet Feed, % mol
ethylene 1-40 10-35
O2 3-12 6-10
CO2 2-40 3-15
ethane 0-3 0-3
Ballast (methane and/or nitrogen)
Balance
chloro-moderator, ppmv total
0.1-20 0.5-15
Coolant temperature, °C.
175-315 205-290
Catalyst temperature, °C.
185-325 215-300
O2 conversion level, %
10-60 20-60
EO Production (Work Rate,
2-25 5-20
lbs. of EO or its equivalent/cu. ft. of
catalyst per hour)
______________________________________
*Liters of gas at standard temperature and pressure passing over one lite
of packed catalyst per hour.

The ranges and limitations provided in the instant specification and claims are those which are believed to particularly point out and distinctly claim the instant invention. It is, however, understood that other ranges and limitations that perform substantially the same function in substantially the same manner to obtain the same or substantially the same result are intended to be within the scope of the instant invention as defined by the instant specification and claims.

The following example is provided as a means to illustrate the process of the instant invention and is not to be construed as limiting the invention.

In the following example reactor A represents a fixed bed tubular ethylene oxide reactor with recycle loop to which the prechloriding technique of this process was applied. Reactor B represents the same type of reactor which was started up in a conventional fashion without the application of the prechloriding technique of this invention. The following description describes the treatment of Reactors A and B prior to start-up.

An alumina-supported silver catalyst containing cesium as a promoter was loaded into the reactor. The reactor was then subjected to a nitrogen heat treatment to remove ammonia and amines from the fresh catalyst. The reactor was heated to about 420°-430° F. (216°-221°C) utilizing the reactant coolant heater during which heat-up nitrogen gas was circulated through the recycle loop. Nitrogen flow was continued for about 70 hrs., at which point the ammonia concentration fell below 10 ppmv.

After removal of the nitrogen-containing compounds from the catalyst, the reactor recycle loop was pressurized with ethylene and nitrogen in preparation for prechloriding and/or start up. A gas flow rate of approximately design flow rate was maintained in the reactor and the ethylene concentration was controlled at about 10% v.

Ethyl chloride was then added to the inlet of reactor A at a rate of about 150 milliliters per hour. The reactor temperature was controlled at about 370°-380° F. (188°-193°C) The chloride concentration in the recycle loop increased rapidly and stabilized at about 8-9 ppmv. The prechloriding of the reactor was continued for about 6 hours, at which point about 1.2 milliliters of liquid ethyl chloride per cubic foot of catalyst had been added to the reactor. Ethylene concentration then was brought up to about 15% mol.

The reactor was then started up by adding oxygen to the reactor, adjusting the ethyl chloride level to provide a concentration of about 1 ppmv in the recycle loop and raising the temperature. The ethylene oxide reaction started at about 405° F. (207°C) and about 1% v oxygen. Temperature, chloride levels and oxygen concentrations were adjusted over the next 60 hours to bring the reactor to design operating levels.

Reactor B Start-Up

Reactor B was started up by adding oxygen to the reactor gases of nitrogen and ethylene, and increasing the temperature. The ethylene oxide reaction started at about 390° F. (199°C). Ethyl chloride was then started at a rate of about 100 milliliters per hour, gradually lowering the rate to maintain about 1 ppmv of chloride in the recycle loop. Temperature, chloride levels and oxygen concentrations were adjusted over the next 100 hours to bring the reactor to design operating levels which were the same as in Reactor A.

As noted above, the prechlorination step of the instant process allowed Reactor A to be brought up to design operating levels in about 60 hours; whereas, it took about 100 hours to bring the non-prechlorided Reactor B to the same design operating levels. Thus, the instant process shortened the normal start-up time by about 40 hours, thereby providing a significant commercial advantage. In a large scale commercial operation, shortening the start-up process by several days can be worth several hundreds of thousands of dollars to the plant operator.

The ethylene oxide selectivity (moles of ethylene oxide produced/moles of ethylene consumed) was measured during the start-up as a function of time. These results are shown in FIG. 2 for the start-up process of this invention and a conventional start-up process. As can be seen from this Figure, the instant process allowed optimum selectivities to be reached in about a third of the time of that required by the conventional process.

Oxygen conversions were also measured during start-up. During steady operations oxygen conversion levels will normally be held at about 30-40%. However, during conventional start-up, due to the high activity of the catalyst, the oxygen conversions will initially overshoot design limits. Extremely high oxygen conversions can result in hot spots in the catalyst which can decrease its life due to sintering. The start-up procedure of the instant process results in peak oxygen conversion levels during start-up some 30% lower than the conventional start-up. This damping of the start-up oxygen conversions will, it is believed, contribute to a longer life for the catalyst.

Patel, Jitendra G., Johnson, Beamon M., Shankar, Pettai K.

Patent Priority Assignee Title
10040055, Jun 02 2015 SCIENTIFIC DESIGN COMPANY, INC Epoxidation process
10449520, May 15 2017 SCIENTIFIC DESIGN COMPANY, INC Porous bodies with enhanced crush strength
10512894, Jun 02 2015 Scientific Design Company, Inc. Porous bodies with enhanced pore architecture
10532989, May 09 2007 SHELL USA, INC Epoxidation catalyst, a process for preparing the catalyst, and a process for the production of an olefin oxide, a 1,2-diol, a 1,2-diol ether, a 1,2-carbonate, or an alkanolamine
10751699, Jun 02 2015 Scientific Design Company, Inc. Porous bodies with enhanced pore architecture
11059017, Sep 15 2017 MULTIPHASE SOLUTIONS, INC Halogen selective detection gas chromatography for the on-line analysis and control of selective oxidation chemical production processes
11801493, Dec 02 2016 SHELL USA, INC Methods for conditioning an ethylene epoxidation catalyst and associated methods for the production of ethylene oxide
5770746, Jun 23 1997 LYONDELL CHEMICAL TECHNOLOGY, L P Epoxidation process using supported silver catalysts pretreated with organic chloride
6455713, Sep 14 1998 Eastman Chemical Company Reactivation of Cs-promoted, Ag catalysts for the selective epoxidation of butadiene to 3,4-epoxy-1-butene
7102022, Jun 28 2002 SHELL USA, INC Method for the start-up of an epoxidation process and a process for the epoxidation of an olefin
7193094, Nov 20 2001 Shell Oil Company Process and systems for the epoxidation of an olefin
7326810, Aug 07 2000 Nippon Shokubai Co., Ltd. Method for starting up reactor
7348444, Apr 07 2003 Shell Oil Company Process for the production of an olefin oxide
7485597, Jun 28 2002 SHELL USA, INC Method for improving the selectivity of a catalyst and a process for the epoxidation of an olefin
7553980, Sep 26 2007 SD Lizenzverwertungsgesellschaft mbH & Co. KG Process for initiating a highly selective ethylene oxide catalyst
7657331, Nov 20 2001 Shell Oil Company Process and systems for the epoxidation of an olefin
7657332, Nov 20 2001 Shell Oil Company Process and systems for the epoxidation of an olefin
7696368, May 11 2007 SD LIZENZVERWERTUNGSGESELLSCHAFT MBH & CO KG Start-up of high selectivity catalysts in olefin oxide plants
7932407, Apr 01 2003 Shell Oil Company Olefin epoxidation process and a catalyst for use in the process
8148555, Jun 26 2003 SHELL USA, INC Method for improving the selectivity of a catalyst and a process for the epoxidation of an olefin
8362284, Apr 21 2009 Dow Technology Investments LLC Method of achieving and maintaining a specified alkylene oxide production parameter with a high efficiency catalyst
8389751, Apr 21 2009 Dow Technology Investments LLC Simplified method for producing alkylene oxides with a high efficiency catalyst as it ages
8487123, Dec 23 2009 Scientific Design Company, Inc. Process for initiating a highly selective ethylene oxide catalyst
8513444, Apr 21 2009 Union Carbide Chemicals & Plastics Technology LLC Epoxidation reactions and operating conditions thereof
8530682, Dec 17 2009 Scientific Design Company, Inc.; SCIENTIFIC DESIGN COMPANY, INC Process for epoxidation start-up
8546592, Sep 29 2010 SHELL USA, INC Olefin epoxidation process
8624045, Dec 17 2009 Scientific Design Company, Inc.; SCIENTIFIC DESIGN COMPANY, INC Process for olefin oxide production
8742146, Dec 08 2010 Shell Oil Company Process for improving the selectivity of an EO catalyst
8742147, Dec 08 2010 Shell Oil Company Process for improving the selectivity of an EO catalyst
8815769, Apr 11 2011 Dow Technology Investments LLC Process for conditioning a high efficiency ethylene oxide catalyst
8845975, Dec 28 2009 Dow Technology Investments LLC Method of controlling the production of silver chloride on a silver catalyst in the production of alkylene oxides
8859792, Sep 27 2011 SHELL USA, INC Olefin epoxidation process
8883675, May 17 2010 Scientific Design Company, Inc.; SCIENTIFIC DESIGN COMPANY, INC Method for making a highly selective ethylene oxide catalyst
8921586, May 07 2008 SHELL USA, INC Process for the production of an olefin oxide, a 1,2-diol, a 1,2-diol ether, a 1,2-carbonate, or an alkanolamine
8987483, Dec 15 2010 The Dow Chemical Company; Dow Technology Investments LLC Method of starting-up a process of producing an alkylene oxide using a high-efficiency catalyst
9067902, Jan 11 2013 SCIENTIFIC DESIGN COMPANY, INC Epoxidation process with post-conditioning step
9096563, Dec 31 2012 Scientific Design Company, Inc. Start-up process for high selectivity ethylene oxide catalysts
9174928, Apr 29 2011 SHELL USA, INC Process for improving the selectivity of an EO catalyst
9346774, May 07 2008 Shell Oil Company Process for the start-up of an epoxidation process, a process for the production of ethylene oxide, a 1,2-diol, a 1,2-diol ether, a 1,2-carbonate, or an alkanolamine
Patent Priority Assignee Title
2194602,
2219575,
2279469,
2279470,
2765283,
3962136, Jan 07 1972 Shell Oil Company Catalyst for production of ethylene oxide
4010115, Jan 07 1972 Shell Oil Company Catalyst for the oxidation of ethylene to ethylene oxide
4810689, Jun 06 1986 Imperial Chemical Industries PLC Process for the preparation of a catalyst for the production of alkylene oxides
4822900, Sep 12 1984 Imperial Chemical Industries PLC Production of ethylene oxide
4831162, Jun 25 1984 Mitsui Toatsu Chemicals, Incorporated Preparation process of ethylene oxide
4874879, Jul 25 1988 Shell Oil Company Process for starting-up an ethylene oxide reactor
4950773, Jan 28 1988 Eastman Chemical Company Selective epoxidation of olefins
////
Executed onAssignorAssigneeConveyanceFrameReelDoc
Dec 02 1991SHANKAR, PETTAI K Shell Oil CompanyASSIGNMENT OF ASSIGNORS INTEREST 0061960174 pdf
Dec 02 1991PATEL, JITENDRA G Shell Oil CompanyASSIGNMENT OF ASSIGNORS INTEREST 0061960174 pdf
Dec 02 1991JOHNSON, BEAMON M Shell Oil CompanyASSIGNMENT OF ASSIGNORS INTEREST 0061960174 pdf
Dec 05 1991Shell Oil Company(assignment on the face of the patent)
Date Maintenance Fee Events
Mar 04 1996M183: Payment of Maintenance Fee, 4th Year, Large Entity.
Mar 31 2000M184: Payment of Maintenance Fee, 8th Year, Large Entity.
Apr 04 2000ASPN: Payor Number Assigned.
Mar 15 2004M1553: Payment of Maintenance Fee, 12th Year, Large Entity.


Date Maintenance Schedule
Oct 13 19954 years fee payment window open
Apr 13 19966 months grace period start (w surcharge)
Oct 13 1996patent expiry (for year 4)
Oct 13 19982 years to revive unintentionally abandoned end. (for year 4)
Oct 13 19998 years fee payment window open
Apr 13 20006 months grace period start (w surcharge)
Oct 13 2000patent expiry (for year 8)
Oct 13 20022 years to revive unintentionally abandoned end. (for year 8)
Oct 13 200312 years fee payment window open
Apr 13 20046 months grace period start (w surcharge)
Oct 13 2004patent expiry (for year 12)
Oct 13 20062 years to revive unintentionally abandoned end. (for year 12)